Objective-C是在C的基础上加入了面向对象的特性，而C#是由C和C++派生而来，可见C#显得更“高级”一些. 1. Objective-C is a strict superset of C 2. Single inheritance 3. Protocols define behavior that cross classes 4. Dynamic runtime 5. Loosely typed 1. C#是全新设计的，没有什么superset。 2. 单继承。 3. 感觉就象C#的interface. 4. 应该是相对C语言来说的，不同于link的方式，ObjC使用了基于消息传递(message-passing)的方式进行方法调用。 5. C#中的用object定义和传递变量应该算上Loosely。
Message Expression
[reciever message] [reciever message:argument] [reciever message:argument andArg:arg2] Metho definition - (void)castBallot; - (int)arg; - (void)setArg:(int)age; - (void)registerForState:(NSString*)state party:(NSString*)party;
对于C#开发人员，这样的代码看起来很诡异，别紧张，把它想象成方法调用就对了。 Objective-C 2.0 introduced dot syntax float height = [persion height]; float height = persion.height; [persion setHeight:newHeight]; persion.height = newHeight; [[persion child] setHeight:newHeight]; persion.child.height = newHeight;
也许是为了ObjC看上去不那么“诡异”，终于看上去“正常”了一些吧~！ id anObject; Persion *aPersion = (Persion *)anObject;
这是所谓的“Loosely typed”吧，id应该是一个指象对象的指针吧。 nil if(persion == nil) return; if(!persion) return; persion = nil; [button setTarget: nil]; persion = nil; [persion castBallot];
nil就是C#里的null，不同的是OjbC中nil上调用方法不出错，对照mesage-passing方式，就好理解了，不就是没人接收消息嘛，那就什么也不做好了。 When ObjC was developed, C has no boolean type (C99 introduced _disibledevent=> BOOL flag = NO;
OjbC没有bool类型，通常使用YES和NO，也可以使用TRUE和FALSE，或者干脆使用0和1表示。 SEL SEL action = [button action]; [button setAction:@selector(start:)]; Conceptually similar to function pointer - (void)setName:(NSString*)name age:(int)age; SEL sel = @selector(setName:age:);
感觉很象C#中的委托(delegate). Class: Class myClass = [myObject class]; NSLog(@"My class is %@", [myObject className]); if ([myObject isKindOfClass:[UIControl class]]) { // something } if ([myObject isMemberOfClass:[NSString class]]) { // someting string specific }
C#中有Type, 上面的代码在C#中如下： Type myClass = myObject.GetType(); Console.WriteLine(string.Format("My class is {0}", myClass.TypeName)); if(myObject.GetType() == typeof(UIControl)) { // something } if (myObject is typeof(String)) { // someting string specific }
Identity versus Equality Identity - testing equality of the pointer values if (object1 == ojbect2) { NSLog(@"Same exact object instance"); }
Equality - testing object attributes if ([object1 isEqual: object2]) { NSLog(@"Logically equivalent, but may be different object instances"); }
C#中好象没有直接比较对象属性值的功能，得自已override Equals方法。
description:
- (NSString*)description; [NSString stringWithFormat: @"The answer is: %@", myObject]; NSLog([anObject description]);
这不就是object的ToString()方法吗？！ NSObject 对等于C#中的Object类。 NSString In C constant strings are "simple" In ObjC constant strings are @"just as simple" NSString *aString = @"Hello World!"; NSLog(@"I am a %@, I have %d items", [array className], [array count]); NSString *myString = @"Hello"; NSString *fullString; fullString = [myString stringByAppendString:@" world!"];
fullString would be set to "Hello World!". - (BOOL) isEqualToString:(NSStirng*)string; - (BOOL) hasPrefix:(NSString*)string; - (int)intValue; - (double)doubleValue;
基本上没什么好说的，这就是System.Stirng. Common NSMutableString methods: + (id)string; - (void)appendString:(NSString*)string; - (void)appendFormat:(NSString*)format, ...;
示例： NSMutableString *newString = [NSMutableString string]; [newString appendString:@"Hi"]; [newString appendFormat:@" , my favorite number is: %d", [self favoriteNumber]];
是不是很象StringBuilder? Collections Array, Dictionary, Set Common NSArray methods: + arrayWithObjects:(id)firstObj, ...; //nil terminated!!! - (unsigned)count; - (id)objectAtIndex:(unsigned)index; - (unsigned)indexOfObject:(id)object;
NSNotFound returned for index if not found if ([array indexOfObject:@"Purple"] == NSNotFound) { NSLog(@"No color purple"); }
NSNotFound不就是-1吗？！ NSMutableArray NSMutalbeArray subclasses NSArray. Common NSDictionary methods: + dictionaryWithObjectsAndKeys:(id)firstObject, ...; - (unsigned)count; - (id)objectForKey:(id)key;
nil returned if no object found for gived key. NSMutalbeDictionary NSMutalbeDictionary subclasses NSDictionary. Common NSSet methods: + setWithOjbects:(id)firstObj, ...; //nil terminated - (unsigned)count; - (BOOL)containsObject:(id)object;
No object is ever in there more than _disibledevent=> for (Persion *persion in array) { NSLog([persion description]); }
C#的foreach就对了。 Common NSNumber methods: + (NSNumber*)numberWithInt:(int)value; + (NSNumber*)numberWithDouble:(double)value; - (int)intValue; - (double)doubleValue;
NSData/NSMutableData NSDate/NSMutableDate byte[] 和 DateTime就对了。 Class interface declared in header file #import
Class Implementation write in .m file #import "Persion.h" @implemetation Person - (int)age { return age; } - (void)setAge:(int)value { age = value; } // ... and other methods - (BOOL)canLegallyVote { return ([self age] >= 18); } - (void)castBallot { if([self canLegallyVote]) { // do voting stuff } else { NSLog(@"I'm not allowed to vote!"); } } @end
还是感觉一个类一个文件简洁。 SuperClass methods - (void)doSomething { // Call superclass implementation first [super doSometing]; // Then do our custom behavior int foo = bar; // ... }
ObjC super 等于 C# base Object Creation + alloc Class method that knows how much memory is needed. - init Instance method to set initial values, perfomr other setup. Create = Allocate + Initialize Persion *persion = nil; Persion *persion = [[Persion alloc] init];
不就是new个对象吗？！还搞成这样？？！！！ Implementing your own - init method #import "Persion.h" @implementation Person - (id)init { // allow superclass to initialize its state first if (self == [super init]) { age = 0; name = @"Bob"; // do other initialization... } return self; } @end
Multiple init methods - (id)init; - (id)initWithName:(NSString *)name; - (id)initWithNameAndAge:(NSString *)name age:(int)age;
Less specific _disibledevent=> - (id)init { return [self initWithName:@"No Name"]; } - (id)initWithName:(NSString *)name { return [self initWithNameAndAge:name age:0]; }
Persion *persion = [[Persion alloc] init]; // ... [persion release]; // Object is deallocated [persion doSomething]; // Crash! persion = nil; [persion doSomething]; // No effect
Implementing a -dealloc method #import "Persion.h" @implementation Persion - (void)dealloc { // Do any cleanup that's necessary // ... [name release]; // when we're done, call super to clean us up [super dealloc]; } @end
构造函数和析构函数。 Object Ownership #import "Persion.h" @implementation Persion - (NSString *)name { return name; } // retain - (void)setName:(NSString *)newName { if (name != newName) { [name release]; name = [newName retain]; // name's retain count has been bumped up by 1 } } // copy - (void)setName:(NSString *)newName { if (name != newName) { [name release]; name = [newName retain]; // name's retain count has been bumped up by 1 } }
Returning a newly created object - (NSString *)fullName { NSString *result; result = [[NSString alloc] initWithFormat:@"%@ %@", firstName, lastName]; [result autorelease]; return result; }
Autorelease is not garbage collection, Objective-C _disibledevent=> @property int age; @property (copy) NSString *name; @property (readonly) BOOL canLegallyVote;
Synthesizing Properties - (int)age { return age; } - (void)setAge:(int)value { age = value; } - (NSString *)name { return name; } - (void)setName:(NSString *)value { if(value != name) { [name release]; name = [value copy]; } }
@implementation Person @synthesize age; @synthesize name; - (BOOL)canLegallyVote { return (age > 17); }
Memory namagement policies @property (assign) NSString *name; // pointer assignment @property (retain) NSString *name; // retain called @property (copy) NSString *name; // copy called
Property Names vs. Instance Variables @interface Persion : NSObject { int numberOfYearsOld; } @property int age; @end
@implemetation Persion @synthesize age = numberOfYearsOld; @end
就是property没什么说的。 Method type identifier 类方法：+ 实例方法: - ObjC 的+ 等于 C#中的static, 不过ObjC中没有public和 private。
参考学习资料：
http://v.163.com/special/opencourse/iphonekaifa.html
http://rotator.youkulabs.com/?f5527199o1p0
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